Yellowstone National Park has two of the last remaining genetically pure wild bison herds in the nation, which used to roam the continent until humans almost wiped them out by the early 20th century. While most current bison have some cattle genes — a result of interbreeding so western ranchers could make hardier cattle – Yellowstone’s American bison are genetically uninterrupted. But they’re difficult to take out of the park for herd-restoration efforts, because they’re susceptible to catching and spreading a wide range of diseases.

In this new case, researchers were able to take out a purebred developing embryo, wash it clean of disease and implant it into a surrogate commercial buffalo. Unlike the Yellowstone cows, this cow can go wherever veterinarians want to take it. In this case, it was shipped off to the Bronx.

Last fall, Colorado State University reproductive physiologist Dr. Jennifer Barfield and her team took a purebred embryo from a Yellowstone bison cow that lives at an animal health research center in Fort Collins, Colo. (Full disclosure: Your correspondent is an alumna of Colorado State.) Barfield was able to “wash” it so it could not spread diseases like brucellosis, which causes bison to spontaneously miscarry their young. It’s not clear exactly how they washed it (we are awaiting further detail).